A number of devices exist by which engines can be immobilised to prevent theft or misuse of a vehicle or machinery etc. Many devices are mainly concerned with the locking or disconnection of electrical circuits associated with the engine which prevents the engine from being activated. It has been found that most or all the currently available methods which utilise the locking or disconnection of engine electrical circuits in vehicles can be over-ridden, by-passed or otherwise neutralised so allowing the theft or misuse of the vehicle.
Vehicles can also be immobilised with varying degrees of success using mechanical devices ranging from steering wheel and brake locks to lockable fuel valves.
French Patent Specification No. 2138170 (Emca Reg. Trust), German Patent Specification No. 640 533 (A. H. Adelsohn, J. F. Hultman), French Patent Specification No. 2647 877 (Alexanare Yanacopoulo), also disclose key actuated lockable fuel valves. Similarly, British Patent Specification Nos. 2 196 413 (Spouse), 130 344 (Emca Reg. Trust), 988 912 (Ross Courtney and Company Limited, 422 494 (Adelsohn), 190 832 (Hopkins) and U.S. Pat. No. 3,885,586 (Tibbets) and U.S. Pat. No. 3,838,587 (Good) all describe various types of fuel valves to prevent vehicle theft.